GETTING STARTED IN HOME CINEMA, PART ONE
Recreating the experience of watching a movie in a cinema,
at home is not new idea. Rich people with big houses have been doing it for
years, but now anyone can join in the fun. You don't need a lot of money
either, or a vast amount of room, all it takes is a little determination and
planning. The equipment is readily available and easy to use, the only real
problem is deciding which way to go. That’s where we come in. This four-part
series has been designed to guide you through the maze of technical jargon, marketing-speak,
and plain old waffle, to help you make the right decisions.
Home cinema is no longer a luxury. If you have a reasonably
recent TV, video and hi-fi, you could already have most of the components for a
worthwhile system; or maybe you want to start from scratch. In either case home
cinema can transform your viewing enjoyment. It puts you and your family in the
best seats in the house, watching the movies you want to see, when you want to
see them, what’s more the popcorn and fizzy drinks are a whole lot cheaper...
AN IMMEDIATE IMPROVEMENT
Even if the concept of full-blown home cinema holds no
interest, you surely want to get the best picture and sound performance from
your present set-up. If you have a stereo TV, VCR and satellite receiver -- or
all three -- connected together only by aerial leads, then you are almost
certainly missing out. Virtually all TV and video equipment built within the
past eight to ten years have specialised SCART sockets on the back panels, carrying
unadulterated audio and video signals. By connecting equipment together using a
simple SCART to SCART leads, costing around five pounds, large chunks of circuitry inside the TV are
by-passed, eliminating noise and other undesirable by-products of signal
processing, making a noticeable improvement to picture and sound quality.
If you have a stereo satellite receiver -- most models are
these days -- and/or a NICAM VCR, but your television is a mono model, you
don’t have to miss out on stereo sound, if you also have a hi-fi system. Most
audio and video systems can be simply connected together using one or two
inexpensive connecting leads. For the best effect place the hi-fi speakers a
foot or two either side of the TV screen and connect the line-audio outputs
from the VCR and satellite receiver to one of the auxiliary inputs on the hi-fi
system amplifier. Most audio and video devices use simple push-fit phono (aka
RCA or ‘cinch’) connectors; they’re conveniently colour-coded red and black (or
white). It takes just a few minutes, and a little reorganisation, but the
difference it makes can be quite remarkable. In the case of a NICAM VCR it
means you will be able to watch TV programmes, and pre-recorded movies in
stereo, without having to go to the expense of buying a new television.
3D PHONIC AND OTHER TECHNOLOGIES
One of the major disadvantages of home cinema is the
apparent need for lots of extra boxes and wires all over the place. Whilst it
is true that you do need additional loudspeakers, to faithfully reproduce the
acoustics of a large auditoria or theatre, research into the way we perceive
sound, and recent advances in digital signal processing (DSP) mean it is now
possible to create some quite impressive spatial and surround-sound effects,
using just two speakers.
3D effects systems are now featured on a number of
televisions and home cinema hi-fi systems. A variety of techniques are used,
from simple stereo wide, which increases the apparent width of the stereo
image, to replicating multi-channel cinema sound systems. The usual trick is to
add in extra sounds to the original right and left stereo channels. A small
portion of the signal is electronically delayed, for a few milliseconds,
mimicking the low-level, almost subliminal sounds, that are reflected back to
the listener from distant walls and the ceiling, creating a feeling of space.
Most DSP systems work on the basic stereo soundtrack, or create pseudo stereo
and surround effects from mono sources, some top-end models are able to extract
surround-sound information hidden in the soundtrack.
In all cases the basic laws of acoustics still apply and
whilst is possible to create a sensation of sounds coming from somewhere other
than the main loudspeakers, they cannot perform miracles and actually localise
sounds behind the listening position. Most 3D systems also produce a fairly
narrow and shallow ‘sweet spot’ where the effect will be most noticeable, and
the shape of the room and proximity of walls can affect the shape of the
soundstage. Nevertheless, if a full blown multi-channel surround-sound system
is out of the question, or your living room
is on the small side, they are
RECOMMENDED 3D TVs
JVC AV-21AX2EK, 21-inch NICAM TV £400 (25 and 29-inch TVs
JVC have developed a hybrid Dolby Pro Logic system, called
3D Phonic, that processes and mixes movie surround sound information in with
the stereo soundtrack. 3D Phonic TVs can also be upgraded to full multi-channel
operation by adding extra amplifiers and speakers
SHARP 51DS05H, 21-inch NICAM TV, £350 (25-inch model also
Sharp use the SRS (sound retrieval system) to create a wide
pseudo-surround soundfield. This works well with mono and stereo sources, and
movie soundtracks with a lot of dynamic effects.
WHAT IS DOLBY PRO-LOGIC?
Once you’ve started your journey into home cinema you will
quickly encounter the mighty and mysterious Dolby Pro-Logic or ‘DPL’. There’s a
lot of confusion and mis-information around, so here are the plain facts. Dolby
Pro Logic is four-channel surround-sound decoding and processing system,
developed by Dolby Laboratories in the US. It should not to be confused with
Dolby B or C noise processing, which is something quite different. DPL decoders
are now fitted to a wide range of televisions and mini hi-fi systems, plus a
handful of VCRs and satellite tuners. They’re also available as stand-alone
components and upgrade kits, for existing home entertainment set-ups.
A DPL decoder’s job is to extract the four audio channels
contained within the stereo soundtrack of several thousand movies made since
the mid 1970s. The movies in question have what is known as a Dolby Stereo
soundtrack; the first major film to be recorded in Dolby Stereo was Star Wars,
released in 1972.
The four audio channels comprise the normal right and left
stereo, the third is mainly used for dialogue and the fourth carries mostly
sound effects. In a cinema the centre channel is used to focus the audience’s
attention on the screen. This is important in a large movie theatre, especially
for those seated away from the centre-line of the right and left channel
speakers. The rear effects channel is used to create or enhance an atmosphere,
by immersing the audience in sound -- the sound of falling rain or wind for
example -- or to add impact to what’s happening on the screen, with loud
explosions, rumbles. It is also used to emphasise movement, with sounds
following the action, as it moves towards or away from the audience. The four tracks are embedded into a normal
two-channel stereo soundtrack using a phase shifting technique, which doesn’t
affect normal stereo sound reproduction. The original intention was to allow
cinema owners to upgrade to surround-sound, quickly and relatively cheaply, whilst
the same movie prints could still be shown in older, less well-equipped cinemas.
Dolby Stereo was the catalyst for home cinema as we know it
today. Movie fans in the US discovered that the extra channels were carried
across when a movie was transferred on to tape or video disc, or shown on
terrestrial and satellite television, (when broadcast in stereo). Demand for
domestic decoders grew quickly during the early 1980s. First generation
processors were only able to extract the rear surround channel, using ‘passive-matrix’
decoders. Soon after, more advanced four-channel decoders, based on movie
theatre systems began to appear. The cost of ‘active-matrix’ or Dolby Pro-Logic
decoders fell quickly, driven by demand and the rapid increase in the amount of
material. By the late eighties a growing number of television programmes were
produced with Dolby Stereo soundtracks,
though strictly speaking when Dolby Stereo is used on video or TV it should be
referred to as ‘Dolby Surround’.
The four channel outputs from a Dolby Pro Logic decoder are
amplified and used to drive loudspeakers placed either side of, and below the
television screen, (right, left and centre), the fourth surround channel is
normally spit between two speakers placed behind the viewing position.
ADDING DOLBY PRO-LOGIC
The simplest route into home cinema is the so-called ‘one-box
solution’ which refers to the fact that they’re usually packaged or sold in a
single box. Inside there’s usually several boxes, and lots of wires... DPL upgrade kits are generally the cheapest
option, the processor and amplifiers are incorporated into the centre speaker
enclosure, in one case a TV stand/console; a pair of rear surround speakers are
normally supplied, some models include the front stereo speakers as well,
others utilise the TV’s built-in speakers. Prices start at around £150 rising
to more than £700 for the top-performers.
For those looking for a complete home entertainment package
a DPL mini hi-fi system is hard to beat. Most packages include a CD player --
multi-disc autochangers are becoming more common -- twin cassette decks, AM/FM
tuner amplifier, DPL decoder and DSP processor, plus a set of five speakers.
Performance varies, generally in line with price, you can expect pay from
around £400 upwards for a system that can do justice to both audio and video
material, though you can pay more than £1000 for some top-end packages.
DPL decoders turn up all sorts of places, including
satellite receivers, column speakers and sub-woofers, even VCRs. In fact DPL
video recorders make a lot of sense, particularly if space is at a premium.
Akai were the first to market surround sound video recorders, way back in 1989,
they currently have two models, costing £500 and £700 (VS-G2DPL & VS
G2400DPL), they’ve been joined by the Sony SLV-AV100 (£750), a well-specified
DPL AV amplifier, with a built-in VCR.
Philips MX900 DPL upgrade, £230
Everything is built into the centre speaker, it comes with
rear speakers, just plug it into a NICAM VCR and TV and you’re in business
Aiwa NSX-AV75, mini DPL system, £400
Highly-featured, value for money system, bass effects are a
little lightweight but performance is generally good and there’s plenty of toys
to play with
Akai VS-G2DPL, DPL VCR, £500
In addition to being a top-notch home cinema VCR, this model
has the DPL decoder and amplifiers built-in, simply add speakers.
DOLBY PRO LOGIC TVs
A television -- preferably a large screen model -- is the
core component in any home cinema system, and a natural home for a Dolby Pro-Logic
processor. The first models began to appear in 1994, though TVs with simpler,
passive-matrix Dolby Surround decoders, went on sale in the UK some three years
earlier. A DPL television is the ultimate one-box home cinema solution, though
they do come with a few ifs and buts. The most obvious problem is the performance
of the internal speakers.
Most TV cabinets are an acoustically-unfriendly environment.
Cosmetic demands mean that the speakers on many DPL TVs are narrow elliptical
types, mounted either side of the screen. They produce a thin, confined soundfield,
which is the complete opposite of what you want in a surround sound system.
Some set-makers try to beef up the sound with additional processing, spatial
wide modes and a sub-woofer or two, but in the end separate outboard speakers
are the only answer, though not all sets have external speaker connections.
Centre channel speakers are a real headache for DPL TV manufacturers. Some mount them inside the
cabinet, or rely on a ‘phantom’ centre channel, produced by the right and left
speakers. Others fit the centre speaker into the console or stand, or leave it
up to the owner to make their own arrangements. Rear channel speakers are not
much better. They are often poor little things that splutter and gasp when
driven hard, and the supplied connecting leads are always far too short.
The bottom line is that
the speakers on DPL TVs are usually their Achilles heel often having an
adverse effect on performance. It pays to go for models where it is clear the
manufacturers have taken a bit more time and trouble over the design of the
acoustics, or the standard offerings can be easily replaced.
Trailing speaker cables are a problem for some but in the
next few months several companies will be launching cordless RF speakers, using
the newly ratified European standard 863MHz frequency band. Amongst them will be
re-chargeable battery-powered models, with no trailing wires at all.
RECOMMENDED DPL TVs
HITACHI C2848TN, 28-inch NICAM DPL, £850
Dolby Pro Logic and 3D sound, a big TV that looks and sounds
good; cordless IR speakers are available as an option
SHARP 59-CSD8H, 25-inch NICAM DPL, £650
Good value and above average performance; a built-in sub-woofer
adds extra impact to action blockbuster movies
MITSUBISHI CT-28BW2BD, 28-inch widescreen NICAM DPL, £1000
A very attractively priced, and unusually well-equipped
widescreen model; good bass and a lively, articulate DPL processor could make
this one a classic
So far we have covered what can loosely be termed quick and
easy solutions, but are they necessarily the best route into home cinema?
Whilst some package systems and one-box outfits can produce quite pleasing results,
they almost always involve some sort of compromise.
The answer is to put together a system using separate
components of your own choosing, to meet your specific requirements. It needn’t
be expensive either, in fact it can actually work out cheaper than a package
system. You won’t be buying components you don’t want, or already have,
moreover future upgrades will be a lot easier.
Separate home cinema AV systems tend to be based around the
amplifier. Audio-visual or AV amplifiers come in a variety of configurations,
the commonest being a combined multi-channel amplifier with an on-board DPL
decoder. Most AV amplifiers usually include an assortment of pseudo surround
and a DSP effects processor as well. The advantages of an AV amplifier lies in
the integration of four or five channels of matched amplification, together in
one box, simplified switching of source components and ease of use. Prices start
at under £200, but you can expect to pay at least £300 for models with serious
AV receivers are an increasingly popular alternative. They’re
AV amplifiers with a built-in AM/FM tuner. It’s a useful combination of
technologies in a home entertainment system, reducing the box count still
further. The latest models incorporate RDS (radio data system) decoders, often
at little or no extra cost. RDS is a sort of radio teletext service, giving
station and programme information, up to the minute traffic reports and news,
presented on the front panel display. Quality AV receivers cost from around £300
Of course it is possible to build a system around plain
vanilla stereo amplifiers and a separate DPL decoder -- prices start at around
£250 -- and this is the route many purists prefer, but apart from the added
complexity it’s often a case of diminishing returns, when it comes to
performance. The audio capabilities of video tape and disc fall somewhere
between compact cassette and CD, moreover the rear effects and centre dialogue
channels have a limited bandwidth. It is debatable whether there’s much point in
using expensive high-end components to process relatively undemanding audio information
in a basic DPL set-up, though the equation changes somewhat when it comes to
higher-performance THX systems, and it will change once again, as we move
towards digitally-encoded discrete multi-channel surround, that will be a
feature of DVD. More about that too, in later issues. However, there is no
question that it is worth paying a little extra for components that are designed
specifically to do the job, which brings us to home cinema speakers.
We’ll be looking at AV speakers in considerable detail in
the XXX issue but it’s fair to say that they are a breed apart from
conventional hi-fi loudspeakers. Centre channel speakers are critically
important to achieving a convincing surround sound effect; it’s vital that they
match the characteristics of the right and left stereo speakers. All front
speakers should be magnetically shielded, to avoid colour ‘staining’ on the TV
screen. Rear speakers need to produce a widely dispersed soundfield, a variety
of techniques have been developed to meet this need. Lastly, conventional
speakers often lack the bass response needed for home cinema work, so it’s a
good idea to budget for a sub-woofer as well.
Speaker placement is something else we’ll be looking at in
future issues. Suffice it to say that to achieve the best effect you may have
to shift the furniture around a little, and be prepared to put up with a few extra
wires and boxes, but then no-one said this was going to be easy.
Interconnections are a major bugbear for some people but it
needn’t be a problem, if you take time to plan your installation beforehand. To
give you an idea of what to expect we’ve drawn out some of the most commonly
BOX COPY 1
THE HAFLER EFFECT
It may surprise you to know that it’s possible to build a
surround-sound decoder for around a pound. How? Well it all depends on the way
Dolby Surround signals are processed, which in turn goes way back to something
called the Hafler effect, on which the Dolby system is based. To cut a long story
short, the rear effects and centre channels (S or surround and C or centre) are
combined with the right (R) and left (L) stereo channels, to produce two
outputs Rt (right total) and Lt (left total). The four signals exist in the
same space, but are separated in phase. They can be extracted using a
relatively simple technique whereby four speakers are wired together, so that they’re
out of phase with one another (see diagram). All you need is a potentiometer
(volume control), to set rear channel volume. It actually works, though some
effects can be a bit messy, and the centre channel moves around a bit.
BOX COPY 2
Four-channel surround-sound system used on movie soundtracks
Four-channel surround-sound system -- identical to Dolby Stereo
-- but applicable to video and TV soundtracks
Dolby Pro Logic -- four channel active-matrix surround sound
Digital signal processing -- electronically generated spatial
and pseudo surround effects
Digital Versatile (Video) Disc -- 12 cm optical disc system,
capable of storing 4 hours or more of high quality video, and multiple digital soundtracks
Near instantaneously companded audio multiplexing -- high
quality digital stereo sound system used by UK terrestrial TV
Syndicat des Constructeurs d'Appareils Radio Recepteurs et
Televiseurs, 21-pin plug and socket system used on TVs and
VCRs sold within the EC
Technical specifications devised by Lucasfilm, applied to
high quality home cinema equipment, cinema acoustics and movie to tape and disc
R. Maybury 1997 1011